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Hey peeps,

Just wondering if anyone has done a rear bumper cut-out

Follow this link to the clubroadster.net thread

http://clubroadster.net/vb_forum/showthread.php?t=20082



Basically remove a large portion of the rear bumper to allow a better flow of air out the rear and cancel the "parachute" effect.

I myself will probably give it a try, because my rear bumper has a noticeable plastic warp in an awkward location on the right side.

Any thoughts?

I will be doing the same to mine, as I have a spare bumper

Its very common amongst budget NA racecars, though a simple diffuser is much better, in MANY ways.
The bumper cut is very honda-ish. Very rice.
Where as a functional, read-not super pretty, diffuser looks serious and tough IMO.

Dann

Can you give an example of how to build a rear diffuser for my na? That's the reason i came across this thread, as i'm unable to find sufficient data on the diffuser mod.

The easiest way is to get a 2nd hand stock diffuser off a lotus. Mount it. Including some minor bumper cutting.

or use thick ABS plastic.

Essentially most homemade diffuser needs some mounts bolted or welded to the rear subframe. Then, with abs as an example, you mount the front to the subframe, and rivet or similar the rear to the bumper. Have a look and all this will become clear. The angle from the subframe to the bumper is close enough to the 14 odd degrees your after, and again using abs as an example, yoi use a heat gun to curve it. This way the flow will hit it parallel and curve with it, staying attached.

of course you will need some fins however small, even if only to stop it from flexing as it pulls down, and a couple of threaded rods bolted under the carpet in the boot to again stop it from ripping itself off as it pulls down.

I happen to have a rather serious diffuser mould, but have been too poor to purchase the fibreglass etc needed to mould it.

Dann

The easiest way is to get a 2nd hand stock diffuser off a lotus

What you have said is correct, my two main issues are:

1) Aftermarket Lotus parts are difficult at best to buy, I have been after a set of good probax seats for awhile, let alone a diffuser.
2) I'm not the best at moulding plastic at the moment.

I'll keep looking at it, but in the mean time i think i'll DIY the rear cut out

moulding the abs is easy. Heat it with a heat gun and bend it.

Its a slowish process so you cant ruin it.

Dont get an aftermarket lotus diffuser. Ask the guys at the next track day who is upgrading to call you when they do to offset their costs.

Dann

I've been reading a bunch if other forums and it appears to be a common mod particularly in the US.

I've also thought about this for two reasons - if it works, it's a cheap mod and secondly, if not over done I think it looks pretty good (but like the car in Hjt's pic) you need a pretty clean underside to show-off!

Not sure I want to take off that much though...not prepared to get rid of the foam block behind the bumper.

Anyone else tried this here?

It would be interesting to see some local car build threads for this mod to NA and NB, since it appears we have some willing guinea people!

Apu and HJT, have you asked the MX5 Mania people like David?
How about other places who cater to the MX5 racer?

How about fabricating using some aluminium sheet? Can it be done at an affordable cost?

Haven't had the chance to talk to David yet but will do so. Less concerned about a diffuser as I won't get the full benefit of it.

The diffuser is sooo cheap and easy, why wont you get the full benefit?

Dann

Too much time required on my part (not much of that available with 2 kids) and I probably won't go to the track enough...at least not that I can see at this moment.

One piece of abs for cheap as. A heat gun a stanley knife and half an hour on stands.

It will be faster than a bumper cut because it doesnt need to be perfect cuts etc as you cant see it.

it also has all the same benefits


Dann

See if HJT wants to do a group mod!

Would it be worthwhile for whoever wants to DIY one for us to group buy and then fabricate in one place? A few hands making it faster and potentially better than each person trying to work it out?

I have a serious diffuser mould, all the right angles and curves. ready to mould in fibreglass or carbon. It has a chord or 600mm and a working width of 1200mm.

It should work damn close to a small wing.
When I make one Ill make a heap and flog them off for cheap.

If anyone close by wanted to borrow it and make their own now if you have fibreglass be my guest.









Dann